Hypodermic pressure manometer



M 8 \I/ an N 9 o R 9 0 a up n 5 m% A 2 w mum! Filed NOV. 15, 1949 H RBIERMAN HYPODERMIC PRESSURE MANOMETER Dec. 26, 1950 Patented Dec. 26,1950 UNITED STATES PATENT OFFICE Application November 15, 1949, SerialNo. 127,289 -Claims. (01. 73-389) This invention relates to a hypodermicpressure manometer for measuring intravascular blood pressures and pulsebeat.

Various arrangements have been heretofore suggested and used in aneffort to determine intravascular blood pressures, but the same have haddefinite limitations either structurally, functionally, or economicallythereby limiting either their range of application and usefulness ortheir dependability.

One object of my invention is to provide an improved hypodermicmanometer that is relatively simple but highly effective in determiningintravascular blood pressures over long periods of time.

Another object of my invention is to provide an improved hypodermicmanometer that has a relatively small fluid capacity, a high degree ofmobility, extreme accuracy, variable frequency and sensitivity, freedomfrom changes of body and ambient temperatures, and rapid and simpleelectrical calibration and standardization.

A further object is to provide an improved hypodermic manometer that hasthe foregoing characteristics, that allows the pulse beat to be visuallyobserved, and that provides a multiple infusion or flushing arrangement.

. Other objects and advantages will be apparent to those skilled in theart from the following description of the accompanying drawings inwhich:

Fig. 1 is a perspective of my improved manometer;

Fig. 2 is an enlarged plan view of my manometer; and

Fig. 3 is an enlarged vertical section taken substantially on the line3-3 of Fig. 2.

In the particular embodiment of the invention disclosed herein, I haveprovided a cylindrical, preferably stainless steel, casing I, having apressure and pulse beat chamber 2 closed at one end by a transparentdisc 3 such as Lucite, glass, or the like, held by a threaded ferrule 4.The other end of the chamber is closed by a diaphragm 5, preferablystainless steel, clamped in position by a cap 6 threaded on to casing Ithereby forming a gage chamber '4. The pressure and pulse beat chamber 2has two diametrically opposed openings 2a and 2b. One opening leadsdirectly into a standard three-way stopcock 8 which is an integral partof the device and functions as a flushcock. The other opening leads intoa Luer lock 9 accommodating any standard needle I!) or similar fitting,the needle being inserted into the vascular system of the patient. Toshow the relatively small size of both the device and the capacity ofpressure chamber 2, devices of this type have been made in which thechamber 2 is approximately 2.8 cm. in diameter and 1.5 cm. deep, thetransparent disc 3 is 0.45 cm. thick, and the stainless steel diaphragm5 is 0.02 cm. thick with a surface area of approximately 2.8 sq. cm.Strain responsive impedance means, specifically consisting of bondedwire type strain gages such as shown in Patent No. 2,292,549,diagrammati cally indicated at 12 and I3, are secured to theunder-surface of diaphragm 5 so as to be responsive to changes indiaphragm strains arising from pressure variations in chamber 2. Thegage I2 is preferably centered on the diaphragm so as to be pressureresponsive and the gage I3 is placed tangentially near the diaphragmedge to obtain temperature compensation. Electric conductors 14 extendthrough a suitable opening in the side of cap 6 for connection to thestrain gage l2. An oscillograph or other measuring instrument is used torecord changes in electrical output of the strain gage in response tostrain changes.

In operation, the pressure and pulse beat chamber 2 is filled with aproper solution, such as heparin-saline, to completely exclude air. Thisis accomplished by running the solution, from a suitable reservoirplaced at a desirable height, through the flushcock 8 into the chamberwhile the air is allowed to escape through needle l0. After the stopcockand chamber 2 are filled with the solution to a pressure in excess ofthe intraarterial pressure, the chamber 2 is shut off from the reservoirby closing stopcock 8. If desired, the flow from the reservoir can beregulated so that the needle and chamber are kept filled with thesolution to avoid clotting. However, to record arterial pressure, thechamber 2 is shut off from the solution by closure of stopcock 8.Arterial pressure is then transmitted through needle [0 to theheparin-saline solution in the pressure chamber thereby distending thediaphragm 5 which in turn causes the resistance of strain gage 12 tochange. When actual recordings are not necessary it is best to allow aslow drip of the solution to flow through the needle to maintain itspatency. The transparent disc allows the pulse beat to be observed byreason of blood particles passing through the needle to the small volumechamber 2 and remaining suspended in the solution within the chamber.These particles will oscillate, in response to the pulse beat,sufliciently to be observed through the transparent window. The chamberthus performs simultaneously the dual functions of determining arterialpressure and pulse beat.

The whole apparatus is calibrated initially and need be done only once.For each thickness of diaphragm and strain gage unit, increasing knownpressures are applied to the diaphragm and the output current of thestrain indicator is recorded. If a standardization at ambientatmospheric pressure is desired at that time, a stopcock i5 which isused in the standardization in place of needle I!) should be opencd toroom pressure and stopcock 8 should be closed both to the'chamber and tothe fluid infusing the instrument. There.- fore, the-chamber is atequilibrium with the ambient pressure and unaffected by either the bloodpressure of the infusion pressure. The standardization produces a knownoutput gagecurrent which represents a known pressure. Since thecurrent-pressure relationship islinear, calcula tion of the actualsystolic and diastolic. pressure is a matter of simple proportions. Forexample, with one unit 3.2 milliamperes of output current is equivalentto 120 millimeters of mercury pressurewhen the strain indicator is at 49microns or micro inches maximum sensitivity (Fig. 3). If, during arecording, a 3.6 centimeter deflection is obtained on standardization,vthen 3.6 centimeters is equivalent to'l20 millimeters pressure. If theblood pressure measures 1.2 centimeters from the base line onatmospheric pressure at the peak of systole; and 2.6 centimeter atdiastole, then the blood pressure is 139/86 mm. Hg. The entirestandardization procedure can be completed within three seconds,permitting frequent checks during an. experiment. desired the secondthree-way stopcock. I may be: used to assist in flushing, calibration orother. operations'. For example, both stopcocks may be used with needle10- on the endof the stopcock 15. This is not shown. in Figure. 1,.butis apparent from Figure 2-. Whilerecording prcssures; stopcock l-5isopenfromthe blood vessel throughthe needle to the pressure chamber 2.stopcock 8 is now closed to both ambient air and-theinfusing reservoir.When not recording, the stopcock 8 is open. to the infusing reservoirpreviously referred-:tovaslocated at aproperheight and lead.- ing. tothe chamber, and then through the stope cock. liiand needle Ill intotheblood vessel, thus maintaining patency for the'time until. the recordisl-d'esired' to be taken.

When. calibraticnto. the ambient. air isdesired, stopcock. i5. is opento the. ambientair so that now chamberlisopen to the ambient air throughstopcock. l5. stopcock is closed to the. ambient air and. the reservoirWith-the infusing solution. Of course, it is optional. to use thestopcocks-as described but it has. proved tobeof great advantage to thepractical operationof thisinstrument since not infrequently one wishesto flush out the needle, check ambient air pressures, draw bloodsamples, and even give solutions-throughthis de vice. It thus gains;versatility inoperation which is animportant factor for its-practicaluse.

Asaresult of myimprovedihypodermiclmanometer, the intravascularblood-pressure may be determined inasimple and'accuratemanner over manyhours without any adverse eifects from body or ambient-temperatures.The. small fluid capacity of chamber.2 ,.for the specific dimensions. ofthepdev-ice given, requires a volume change of lessthan-ten cubicmillimeters to record L00. millimeters of mercury. The small. size oftheinstrument and. the flexible leadsfor electrical recording permits. ahighly dssirable degree of mobility for relatively long-v studies.- Manydifferent sensitivities. or. frequencies... butnot necessarily: both,can be obtained. by selecting the 4 proper thickness of diaphragm. Suchdiaphragms, to which gages have already been cemented, can besubstituted easily and quickly. It is thus seen that I have provided avery effective device for the purposes described and one that hasconsiderable practical value.

It will, of course, be understood by those skilled in the art thatvarious changes may be made in tain a pressure transmitting solution, adiaphragm for closing. one end of said chamber, strain responsiveelectrical impedance means mounted-on the surface of said diaphragm onthe outside of said chamber whereby pressure changes in the chambereffect changes in impedance; a transparent closure member for the otherend of said chamber, openings in said chamber o'neof which is to admit:said solution to thechamber to completely fill the same-and the otherofwhich is adapted for connection toa hypodermic needle.

2. The combination set forth in claim I further characterized in thatthe opening through which: the solution is admitted to'the chamber isprovided with a three-way stopcock adapted to allow saidchamber'selectively tocommunic'ate with av source of the solution:through thestop cook or with: the: atmosphere or to entra-p the solutionwithin the chamber.

3. The combination set forth in claim lfurther characterized in that theelectrical impedance-strain gage: means comprises a wire type straingage bonded throughouit its 'effective leng'th to the outside of: thediaphragmr 4: Thecombination set: forth inclaim 1 further characterized:by' the provision of a dia-- phragm; clamping; elementhaving threadedconnection with the casing whereby the: diaphragm maybe readily-removedor inserted.

5. The combination set forth in claim 1 fur-' REFERENGE S GITED Thefollowing references are ofrecord i-n the file of thispatent:

UNITED STATE PATENTS 7 Proc. .oflthesocfor-Experimental. Biology andMedicine, pagev 53; vol.- 56',. 1', May. 194i.

